Agricultural crops are quite susceptible to various types of diseases and damage from soil borne pathogens and subterranean pests, such as nematodes, weeds, fungi, bacteria and insects. To combat such problems, the soil in which the crops are to be planted is commonly treated by a suitable soil fumigant. Such fumigants are volatile products that disperse rapidly through the soil profile to eradicate subterranean pests.
Land to be planted in high value crops is typically first fumigated and then promptly covered with a suitable plastic fumigation film. Such film is designed to retain the fumigant within the planted ground for as long as possible so that the fumigant works most effectively. If a planted field is left uncovered, volatile fumigants are apt to evaporate rapidly into the atmosphere. This tends to significantly reduce the effectiveness of the fumigation. Conventional fumigation films and tarps retard fumigant evaporation so that improved pest eradication is achieved. When crops are planted in rows or beds, the fumigation film is typically applied in disconnected parallel strips, which cover the respective rows. Alternatively, when broadcast fumigation of an entire field is required, a continuous tarp or film must be applied to cover the entire field. This is conventionally accomplished by laying successive plastic strips across the field and sealing the adjoining strips together so that a solid/continuous tarp is formed over the planted crops. In such cases, it is critical that the adjoining strips of film be securely joined to one another. Otherwise, wind is apt to separate the seams and fumigant dissipates into the atmosphere.
Low density polyethylene film (LDPE) and high density polyethylene film (HDPE) have long been used in the fumigation of agricultural fields. When broadcast fumigation is performed, adjoining LDPE or HDPE strips are normally fastened together by an adhesive containing a high percentage of volatile hydrocarbon solvents, also known as volatile organic concentrates (VOC's). When such adhesives are used with LDPE film, they typically achieve tack and are capable of adhering the adjoining strips together within 15-30 seconds. These adhesives tack due to evaporation of the solvent from the adhesive. Nonetheless, LDPE and HDPE polyethylene film tend to be undesirably permeable to many fumigants. Such fumigants can dissipate through the film and move off of the treated field. This significantly reduces the effectiveness of the fumigant and/or greatly increases treatment costs. Recently, virtually impermeable film (VIF) has been adopted for use in the United States and is quickly becoming the standard for row or bed fumigation. VIF film is far less permeable to fumigants than traditional polyethylene film. Unfortunately, VIF film is so impervious that the solvent in standard solvent based adhesives cannot quickly evaporate through the film and adhesive tack. When VOC adhesive is used to join together an adjoining pair of VIF strips, the adhesive requires an undesirably lengthy time to tack sufficiently to secure the strips together. Because the adjoining strips take too long to adhere securely to one another, even a slight amount of wind can cause the adjoining film strips to separate. This, in turn, allows fumigant to escape from the field and through the broken seam of the tarp. Effective fumigation and pest control are therefore frustrated.
Despite their superior fumigant retention capabilities, VIF film, and even more impervious fumigation film known as totally impermeable film (TIF) have not, to date, been adopted for broadcast or solid tarp fumigation. These films simply do not allow currently available high solvent adhesives to tack and seam the film quickly enough to adequately retain the fumigant within the treated soil for proper pest eradication.
In addition to being effectively unusable with VIF and TIF film, conventional high solvent adhesives are also environmentally unfriendly. The use of such adhesives is restricted in certain areas due to governmental regulations that limit the amount of VOCs that can be employed in a given area.